Ratio Of Lecithin Research Articles

Effect of short-chain alcohols as co-surfactants on pseudo-ternary phase diagrams containing lecithin

Lecithin is a natural amphiphilic molecule, the microemulsions of which are often employed as a transdermal delivery medium of drugs and cosmetics. However, it constructs a microemulsion and lamellar phase in a phase diagram without co-surfactant only at a narrow range of composition. In this study, the effect of several short-chain alcohols on pseudo-ternary phase diagrams composed of lecithin, water and dodecane containing 1.0 wt% lidocaine (local anesthetic) was investigated in relation to the application of lecithin-based microemulsion for transdermal drug delivery. The phase diagram for an aqueous solution containing 80.0 wt% ethanol showed a lamellar structure (LC) and bicontinuous isotropic regions. When the mixing ratio of lecithin to alcohols (1-propanol, 1-butanol and n-pentanol) was 2: 1, water-in-oil (L2) and oil-in-water (L1) microemulsions and LC were obtained in a certain range of compositions. The maximum solubilization of water into L2 phase was 38 wt% when the total surfactant was 43 wt% with butanol as cosurfactant.

Effect of Soybean Hulls, Soy Lecithin, and Soapstock Mixtures on Ruminal Fermentation and Milk Composition in Dairy Cows

Two experiments were conducted to determine effects of soybean hulls, soy lecithin, and soapstock mixtures on ruminal fermentation, milk composition, and ruminal microbial populations. In Experiment 1, 20 Holstein dairy cows were assigned to one of five total mixed rations (TMR) in replicated 5 × 5 Latin squares to measure the effect of TMR on intake and milk composition. Four ruminally fistulated cows were used in a 4 × 5 Youden square to measure the effect of TMR on ruminal fermentation. The TMR consisted of 40 or 50% alfalfa and corn silages, 13% soybean hulls, and 47 or 37% of a concentrate containing either 2.25% soybean oil; 2.25% lipid from a mixture of soybean hulls, soy lecithin, and soapstock; or no added lipid. The ratios of soy lecithin to soapstock evaluated were 1:1, 2.5:1, and 4:1 (dry basis). The TMR containing soy lecithin and soapstock at ratios of 1:1 and 2.5:1 resulted in higher milk C18:2 than did the soybean oil TMR. Rate of ruminal NDF digestion of soybean hulls was reduced for the soybean oil TMR.In Experiment 2, a semi-continuous culture system was used to determine effects of soybean oil or an optimal mixture of soy lecithin and soapstock (1:1, wt/wt) on fermentation of soybean hulls and microbial populations. The TMR containing the lipid mixture increased the ratio of acetate to propionate compared with the TMR containing soybean oil and resulted in higher total protozoal counts than did the control TMR. The TMR containing mixtures of soy lecithin and soapstock at ratios of 1:1 and 2.5:1 elevated milk C18:2, and no negative effect on NDF digestion was detected, indicating some degree of ruminal protection.

Distribution of mixtures of bile salt taurine conjugates between lecithin-cholesterol vesicles and aqueous media: an empirical model

Bile salts are surfactants that partition into phospholipid bilayers. When liposomes or membranes are exposed to mixed solutions of bile salts, the more hydrophobic bile salt species associate preferentially with the lipid bilayer. As a consequence, in the aqueous phase, the free monomeric concentration of bile salt declines and the more hydrophilic species become relatively enriched. Above a critical saturating concentration of lecithin-associated bile salt, a phase transition occurs with loss of membrane integrity and formation of mixed micelles. In this paper we present a quantitative model which, for mixed solutions of bile salt taurine conjugates, predicts the distribution of bile salt monomers between large unilamellar vesicles composed of lecithin and cholesterol and the aqueous phase. The model is based on association isotherms for individual bile salts, determined by an ultrafiltration method with empirical curve fitting, and is critically dependent upon the observation that association coefficients of each bile salt are a function of the total bound bile salt/lecithin mole ratio. Given the concentrations of individual bile salts, lecithin and cholesterol, the model permits calculation of the membrane-bound bile salt/lecithin ratio and the concentration of each bile salt remaining free as soluble monomer in the aqueous phase, as well as the overall hydrophilic-hydrophobic balance (hydrophobicity index) of the bile salts remaining free in aqueous solution. Distribution data determined empirically for a variety of mixtures of bile salt taurine conjugates and large unilamellar vesicles of varying cholesterol:lecithin ratio agree closely with predictions. This model may be of value in predicting the physical, biological and toxic properties of mixed bile salt solutions.

Combined Effect of a Lecithin and a Bile Salt on Pancreatic Lipase Activity

Lipolysis is regulated by the presence of amphiphilic compounds such as bile salts and lecithin, which are adsorbed at the triglyceride–water interface and therefore influence the approach of water-soluble pancreatic lipase to its insoluble substrate (emulsified triglycerides). The partition of bile salts between the lipid and the aqueous phase is of prime importance in the expression of lipase activity. Lipase activity was determined as a function of different combinations of concentrations of deoxycholate and dipalmitoylphosphatidyl choline. From ζ-potential measurements, it is evident that lecithin affects the partition of bile salts, most probably by displacing deoxycholate molecules. Our results indicate that lecithin cannot be classified a priori as inhibitor or activator of pancreatic lipase. As an amphiphilic compound, lecithin exerts a synergistic effect with bile salts via the formation of mixed micelles. The final effect on lipolysis depends on the ratio of lecithin to bile salt: low ratios enhance enzyme activity, whereas high ratios lead to inhibition.

1817 Cortical processing of somatosensory information studied by whole-head magnetoencephalogram

Vitamin E TPGS-functionalized polymeric nanoparticles have been developed as a promising drug delivery platform in recent years. Obtaining reproducible monodisperse TPGS/polymeric nanoparticles with high encapsulation efficiency (EE%) still remains a big challenge. In this study, an inverse-phase nanoprecipitation method was developed to synthesize TPGS-functionalized PLGA nanoparticles (TPNs) for controlled release of paclitaxel (PTX). To take advantages of lipids, a part of TPGS in the TPNs was replaced by lipids. The results showed that with weight ratio of TPGS-to-PLGA of 2–3 and a molar replacement of lecithin ratio of 30%, the PTX-loaded TPNs (PTPNs) and PTX-loaded lipid-containing TPNs (PLTPNs) exhibited controllable and nearly uniform size of 130–150 nm and EE% of over 80%. Compared to Taxol®, both the PTPNs and PLTPNs significantly increased the intracellular uptake and exerted strong inhibitory effect on human lung cancer A549 model cells. Furthermore, a selective accumulation to tumor site and significant antitumor efficacy of TPNs in the A549 lung cancer xenografted nude mice were observed by intravenous administration, especially for the PTPNs group. Our data suggested that the inverse-phase nanoprecipitation method holds great potential for the fabrication of the paclitaxel-loaded TPNs and the TPNs prepared here is a promising controllable delivery system for paclitaxel.

Relation between micellar structure of model bile and activity of esterase

In a model bile solution composed of lecithin (L)-bile salt (B), the solubilization of lipid and the accessibility of enzyme to the lipid were examined by observation of EPR spectra and measurement of enzyme activity. The lifetime of the spin probe in the micellar phase was estimated to be approx. 1 μs by means of line shape analysis. Both population and lifetime increased with temperature and the molar ratio of lecithin to bile salt (L/B). The EPR data indicated that simple micelle of bile salt, mixed disk micelle of bile salt-lecithin, and multi-lamellar mixed disk micelle can exist in a model bile solution, depending on the L/B molar ratio across a range from 0 to 1.5. The maximal power of the mixed disk micelle to solubilize cholesteryl ester in the model bile at a L/B molar ratio of 1:1 was confirmed by EPR measurement of cholesteryl 12-DOXYL-stearate. Observation of the enzyme activity on a mixture of model bile and substrate at 37°C revealed selective accessibility of cholesterol esterase (bovine pancreas) to mixed disk micelle, of cholesterol oxidase ( Streptomyces cinnamomeus) to both simple and mixed disk micelle, and of pancreatic lipase (porcine pancreas) to both simple micelle and an oil droplet of substrate. The temperature-dependent activity of cholesterol oxidase to cholesterol in mixed disk micelle can be explained in terms of mesomorphic phase transition of lecithin side chains followed with fluidity of liquid crystal phase. Regarding phospholipase C from Bacillus cereus, though the selective accessibility to the micelles was not observed at 37°C, a decrease in activity for mixed disk micelle could be found at lower temperatures.

Response surface methodology applied to fractionation of de-oiled soya lecithin obtained by supercritical carbon dioxide extraction

Soya lecithin, de-oiled by supercritical carbon dioxide extraction at 200 bar and 50°C, was subjected to ethanol extraction for the enrichment of phosphatidylcholines (PC). The process variables time, temperature and ethanol—lecithin ratio were studied for optimization of PC enrichment by response surface methodology following a Box-Behnken design of experiments. An optimum value of PC enrichment was not found. However, the results indicated: (a) PC enrichment generally increased with an increase in all three variables. (b) Until 5 min extraction time, there is no significant increase in PC enrichment. (c) Above an ethanol—lecithin ratio of 50 L/kg, not much increase in PC enrichment was noticed. (d) A rise in the temperature of extraction leads to increase in PC enrichment.

Structural characterization of the micelle-vesicle transition in lecithin-bile salt solutions

Small-angle neutron scattering (SANS) and dynamic light scattering (QLS) are used to characterize the aggregates found upon dilution of mixed lecithin-bile salt micelles. Molar ratios of lecithin (L) to taurocholate (TC) studied varied from 0.1 to 1, and one series contained cholesterol (Ch). Mixed aggregates of L and taurodeoxycholate (TDC) at ratios of 0.4 and 1 were also examined. In all cases the micelles are cylindrical or globular and elongate upon dilution. The radius of the mixed micelles varies only slightly with the overall composition of lecithin and bile salt which indicates that the composition of the cylindrical micelle body is nearly constant. The transition from micelles to vesicles is a smooth transformation involving a region where micelles and vesicles coexist. SANS measurements are more sensitive to the presence of two aggregate populations than QLS. Beyond the coexistence region the vesicle size and degree of polydispersity decrease with dilution. Incorporation of a small amount of cholesterol in the lipid mixture does not affect the sequence of observed aggregate structures.

Stability study of lecithin liposomes during storage using ESR

The technique of electron spin resonance is employed to study the stability of liposomes by measuring the decay of the encapsulated volume as a function of the incubation time. This volume at first remained constant, next it decreased to 50% of its initial value in a characteristic time t 50%, then it decreased further to a final residual value. The characteristic time varied from 1.2 to 23 days, it was larger for egg yolk than for soybean samples, and for both materials it increased with the lysolecithin to lecithin ratio. The oxidation damage associated with the appearance of hydroperoxides increased with the incubation time, and was twice as large for unilamilar vesicles than it was for multilamilar vesicles. The oxidative decay was three times faster for soybean than for egg yolk samples, but the amount of oxidative damage after the time t 50% was only 10–15% greater for the soybean case. The studies were carried out using the Tempone nitroxide radical ion, and the broadening agent tris(oxalato)chromate(III).

Effect of a soybean hull:soy lecithin:soapstock mixture on ruminal digestion and performance of growing beef calves and lactating dairy cattle

Four experiments were conducted to evaluate the effect of a soybean hull, soy lecithin, and soapstock mixture on ruminal fiber and protein digestion, growth efficiency of beef calves, and lactational performance of dairy cattle. An initial mixing experiment determined that a 4:1 ratio (DM basis) of soy lecithin:soapstock could be added to soybean hulls at 15% (wt/wt, DM basis); this mixture had acceptable mixing and handling characteristics. Dietary addition of a mixture of 85% soybean hulls, 12% soy lecithin, and 3% soapstock (DM basis; SLS) to provide 0, 3, 5, or 7% supplemental fat resulted in a linear (P < .01) decrease in in situ rate of ruminal NDF digestion with no effect on rate of CP digestion. Daily gain, DMI, and feed efficiency (kilograms of gain/kilogram of DMI) of growing beef calves were not affected (P > .10) as graded levels of SLS replaced corn grain. However, as graded levels of SLS replaced soybean hulls, daily gain and feed efficiency increased linearly (P < .01). Based on the results of these trials, Holstein dairy cattle were fed four isonitrogenous and isoenergetic diets that contained either high levels of nonfiber carbohydrates (43%) and no added fat, 1% ruminally inert fat, a 6% level of SLS, or a 12% SLS level (all on DM basis). Efficiency of 4% fat-corrected milk production (kilograms of milk/kilogram of DMI) was greatest for cows fed SLS at 6% of dietary DM. The SLS mixture was an excellent source of fiber and vegetable fat, comparable in feeding value to corn grain, for inclusion in the diets of beef calves and dairy cows.

Influence of total lipid concentration, bile salt:lecithin ratio, and cholesterol content on inter-mixed micellar/vesicular (non-lecithin-associated) bile salt concentrations in model bile.

We modified classic equilibrium dialysis methodology to correct for dialysant dilution and Donnan effects, and have systematically studied how variations in total lipid concentration, bile salt (taurocholate):lecithin (egg yolk) ratio, and cholesterol content influence inter-mixed micellar/vesicular (non-lecithin-associated) concentrations (IMC) of bile salts (BS) in model bile. To simulate large volumes of dialysant, the total volume (1 ml) of model bile was exchanged nine times during dialysis. When equilibrium was reached, dialysate BS concentrations plateaued, and initial and final BS concentrations in the dialysant were identical. After corrections for Donnan effects, IMC values were appreciably lower than final dialysate BS concentrations. Quasielastic light scattering was used to validate these IMC values by demonstrating that lipid particle sizes and mean scattered light intensities did not vary when model biles were diluted with aqueous BS solutions of the appropriate IMC. Micelles and vesicles were separated from cholesterol-supersaturated model bile, utilizing high performance gel chromatography with an eluant containing the IMC. Upon rechromatography of micelles and vesicles using an identical IMC, there was no net transfer of lipid between micelles and vesicles. To simulate dilution during gel filtration, model biles were diluted with 10 mM Na cholate, the prevailing literature eluant, resulting in net transfer of lipid between micelles and vesicles, the direction of which depended upon total lipid concentration and BS/lecithin ratio. Using the present methodology, we demonstrated that inter-mixed micellar/vesicular concentrations (IMC) values increased strongly (5 to 40 mM) with increases in both bile salt (BS):lecithin ratio and total lipid concentration, whereas variations in cholesterol content had no appreciable effects. For model biles with typical physiological biliary lipid compositions, IMC values exceeded the critical micellar concentration of the pure BS, implying that in cholesterol-supersaturated biles, simple BS micelles coexist with mixed BS/lecithin/cholesterol micelles and cholesterol/lecithin vesicles. We believe that this methodology allows the systematic evaluation of IMC values, with the ultimate aim of accurately separating micellar, vesicular, and potential other cholesterol-carrying particles from native bile.

Measurement of the ratio of lecithin to sphingomyelin in amniotic fluid by fast atom bombardment mass spectrometry

We describe a fast atom bombardment mass spectrometric method to determine the ratio of lecithin to sphingomyelin in amniotic fluid. Between m/z 400 and 1000, amniotic fluid extracts showed clear peaks for only sphingomyelin and lecithin. The molecular species of fatty acid in the phospholipids were analyzed quantitatively and quickly in a small volume of the extracts. The dipalmitoyllecithin/palmitoylsphingomelin ratio, determined by the proposed method, showed a reasonable correlation to the lecithin/sphingomyelin ratio measured by thin-layer chromatography. This method allows rapid and sensitive measurement of these phospholipids.

Effects of continuous insulin infusion therapy on lipoprotein surface and core lipid composition in insulin-dependent diabetes mellitus

To determine whether intensive insulin therapy has the same beneficial effects on lipoprotein composition that it has been shown to have in insulin-dependent diabetes mellitus (IDDM) on the routinely measured plasma lipids, we studied 10 patients after 6 months of conventional therapy (CIT) and again after 6 months of therapy with continuous subcutaneous insulin infusion (CSII). While the mean of home blood glucose levels (8.1 ± 0.5 v 7.9 ± 0.5 mmol/L) decreased no further, plasma triglycerides (TG) (CIT, 102.7 ± 25.0; CSII, 89.6 ± 27.1 mg/dL; P < .001) decreased after CSII, and high-density lipoprotein cholesterol (HDL-C) increased significantly, primarily as a consequence of an increase in HDL 2 (CIT, 12.2 ± 6.0; CSII, 18.1 ± 6.3 mg/dL; P < .02). Low-density lipoprotein cholesterol (LDL-C) was unchanged (CIT, 82.2 ± 32; CSII, 84.0 ± 27.8 mg/dL). After CIT, two indices of lipoprotein surface composition were altered: (1) the free cholesterol (FC) to lecithin ratio, which is a new cardiovascular risk factor, was abnormally increased in plasma, very-low-density lipoprotein (VLDL) + LDL, and HDL, and (2) the sphingomyelin to lecithin ratio, an index of the surface rigidity of lipoproteins, was increased in the HDL subfractions. While CSII treatment resulted in favorable changes in whole plasma lipids, it failed to correct these disturbances in composition. Since the participation of lipoproteins in certain steps in reverse cholesterol transport appears to be impaired when their surface constituents are altered, persistence of these disturbances may sustain the increased cardiovascular risk of IDDM patients, even when their clinical control is very good and their plasma lipids are normal.

Comparison of perturbation effect of propranolol, verapamil, chlorpromazine and carbisocaine on lecithin liposomes and brain total lipid liposomes. an EPR spectroscopy study

Effect of verapamil, propranolol, chlorpromazine and carbisocaine on dynamics and/or order of liposomes (perturbation effect), prepared from different molar ratios of lecithin (PC) and rat brain total lipids (TL) was studied by EPR spectroscopy using spin probes 16-doxyl stearic acid and 14-doxyl phosphatidylcholine. The PC liposomes had higher dynamics and/or lower order than the TL liposomes. The perturbation effect of the drugs depended largely on the lipid composition of the liposomes. The drugs at the drug/lipid molar ratios from 0.1 to 1 increased membrane dynamics and/or decreased membrane order. The drugs had the most pronounced perturbation effect in the liposomes prepared from brain total lipids. The effect of the drugs decreased with decreasing the TL PC ratio in the liposomes and was lowest, almost diminished, in the PC liposomes. Increasing concentration of the drugs decreased the difference between the dynamics and/or order of the PC and TL liposomes and so eliminated the influence of lipid composition on these membrane parameters. The results emphasize the role of lipid composition in studies concerning drug-lipid interactions in model and biological membranes.

Probucol treatment in hypercholesterolemic patients: effects on lipoprotein composition, HDL particle size, and cholesteryl ester transfer

Despite probucol's capacity to induce regression of tendinous xanthomata and reduce whole plasma and LDL cholesterol (LDL-C) in patients with hypercholesterolemia, its therapeutic use in the United States has been limited because of concern about its HDL-lowering effects. To assess the possibility that probucol might facilitate mobilization of tissue cholesterol in the presence of low HDL levels as a consequence of favorable changes in lipoprotein composition and function, we have analyzed lipoproteins and studied cholesteryl ester transfer (CET) in hypercholesterolemic patients before and after treatment. Prior to treatment, the free cholesterol (FC)/lecithin (L) ratio in plasma, a new index of cardiovascular risk, and the mass of cholesteryl ester transferred from HDL to the apo B-containing lipoproteins (CET) both were significantly increased ( P < 0.001). As previously shown, plasma cholesterol, LDL-C, HDL-C, HDL 2, and apolipoproteins A-l, A-11 and B all fell significantly following probucol treatment. The FC L ratio in plasma ( P < 0.01) and HDLZ ( P < 0.01) both fell significantly also, as did the sphingomyelin/lecithin ratio in VLDL + LDL ( P < 0.001) which is typically increased in untreated patients with hypercholesterolemia. Nondenaturing gradient gel electrophoresis in 6 patients revealed that the quantitative changes in HDL were associated with a redistribution of particles characterized by a decrease in the prevalence of the largest (HDL 2b) and a relative increase in the number of the smallest (HDL 3b) particles. Moreover, CET following probucol therapy returned to levels which were indistinguishable from those of normolipidemic controls. These results indicate that untreated patients with hypercholesterolemia have abnormalities in (1) lipoprotein composition which have been shown to retard the movement of cholesterol from tissues to HDL, and in (2) CET which is accelerated and can potentially lead to the formation in plasma of atherogenic CE-enriched apo B-containing lipoproteins. Probucol's capacity to reverse these specific alterations suggests that it may have beneficial effects on cholesterol transport in patients with hypercholesterolemia.

Hydrophobic mismatch in gramicidin A'/lecithin systems

Gramicidin A' (GA') has been added to three lipid systems of varying hydrophobic thicknesses: dimyristoyllecithin (DML), dipalmitoyllecithin (DPL), and distearoyllecithin (DSL). The similarity in length between the hydrophobic portion of GA' and the hydrocarbon chains of the lipid bilayers has been studied by using 31P and 2H NMR. Hydrophobic mismatch has been found to be most severe in the DML bilayer system and minimal in the case of DSL. In addition, the effects of hydrophobic mismatch on the cooperative properties of the bilayer have been obtained from 2H NMR relaxation measurements. The results indicate that incorporation of the peptide into the bilayer disrupts the cooperative director fluctuations characteristic of pure multilamellar lipid dispersions. Finally, the GA'/lecithin ratio at which the well-known transformation from bilayer to reverse hexagonal (HII) phase occurs (Van Echteld et al., 1982; Chupin et al., 1987) is shown to depend on the acyl chain length of the phospholipid. A rationale is proposed for this chain length dependence.

Radial "high-performance" thin-layer chromatography used to assess fetal lung maturity

A radial "high-performance" thin-layer chromatographic (HPTLC) method is described by which the percentages and ratios of phosphatidylinositol, sphingomyelin, lecithin, phosphatidylethanolamine, phosphatidylglycerol, and dimethyl phosphatidylethanolamine may be determined simultaneously. An additional method for radial HPTLC determination of saturated phosphatidylcholine is described. We report results of application of these methods to greater than 2000 specimens of amniotic fluid from both diabetic and nondiabetic cases.

Responsiveness of L‐S Ratio of the Amniotic Fluid To Intra‐Amniotic Administran of Thyroxine: Role of fetal age

Since 1982 we have accelerated fetal maturation with intra-amniotic thyroxine (T4) in more than 140 patients. The purpose of this analysis was to determine the rate of change of the ratio of lecithin to sphingomyelin (L/S) after administration of T4 at different gestational ages, and to compare the responses to the first and the second administration of T4. Fifty-nine cases in which administration of T4 was continued for 2 weeks or more, and in which at least 3 determinations of L/S had been performed, were identified. Gestational age of the fetus at the inititiation of treatment ranged from 26 to 31 weeks (mean 29.3 weeks). Thyroxine was administered weekly in 200 to 500 mcg doses. Administration of T4 prior to the 27th week did not change the L/S. From the 27th and 31st week of gestation, the slope of the L/S, after the initial dose of T4 increased from 0.33/wk to 1.05/wk. In contrast the slope of the untreated patients changed little reaching a maximum of 0.22 at the 33 week. L/S greater than 2 was observed in 80% of cases after 2 weeks of therapy, when it had been initiated after the 26th week. The response to the second dose was about twice that of the first in fetuses less than or equal to 30 weeks, but was similar to that seen after the initial dose in fetuses greater than 30 weeks. Phosphatidylglycerol (PG) was detected in amniotic fluid in 51% of cases after 2 weeks of treatment, and in 6 instances as early as at the 30th week. Responsiveness of L/S to T4 treatment of the fetus is a function of gestational age and of prior exposure to T4.

Interactions of lecithin and pig apolipoproteins of high density lipoproteins at the surface monolayer of reconstituted very small particles.

Cosonication of egg yolk lecithin and triolein with apolipoproteins isolated from pig high density lipoprotein (apoHDL) gave us reconstituted high density lipoprotein particles (r-HDLs) of 9 nm in average diameter. They were smaller than microemulsion particles (MEs) composed of the lipids (35 nm). The protein/egg yolk lecithin ratio in the fractionated r-HDLs was higher in the smaller particles. Binding of a hydrophobic probe, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), to MEs, r-HDLs and apoHDL were evaluated on the basis of Halfman and Nishida's method. The reconstitution of apoHDL into MEs led to a 68% reduction in the binding of TNS and a small increase in the alpha-helix content as compared with free apoHDL. The binding experiments also showed the condensation of lecithin molecules at the r-HDL surface. The amphipathic helixes of apoHDL are located in the surface monolayer of egg yolk lecithin surrounding the triolein core. The intercalation of the hydrophobic residues of apoHDL between egg yolk lecithin molecules brings about a pronounced curvature of the surface and a decrease in the particle diameter.

Leakage of sulphobromophthalein from large simple bilayer phospholipid vesicles.

Single bilayer phospholipid vesicles containing entrapped sulphobromophthalein were prepared from a phospholipid film in the presence of deoxicholate at a molar ratio of deoxicholate to phospholipid of 1:2. The trapping efficiency of these vesicles was a function of sulphobromophthalein concentration during incubation, reaching a maximum at a molar ratio of egg lecithin to sulphobromophthalein of 25:1. Release of sulphobromophthalein from liposomes was observed when the vesicles were incubated with bovine serum albumin. The sulphobromophthalein released appeared to be associated with albumin when analysed by Sepharose 4B gel filtration. Leakage of sulphobromophthalein from liposomes was also observed when the vesicles were incubated with different amounts of oleic acid. However, the amount of sulphobromophthalein released from liposomes was much lower than that observed in the presence of bovine serum albumin. These vesicles incorporated up to one molecule of oleic acid for each two and a half molecules of egg lecithin, and appear to be suitable as acceptors in studies of fatty acid transfer between membranes.